In this paper we report the development of the single frequency dye laser as a plasma diagnostic for measuring ion velocity distributions with a resolution limited only by the naturallinewidth of the laser excited resonance transition. For the 6S1!2-6P1!2 transition in Ba+ this corresponds to a velocity uncertainty of 10 3 cm/s. Velocity selection is performed by the laser as it scans the Doppler broadened plasma absorption line, in contrast with the usual method of scanning an emission line with a high-resolution spectrometer. Both sensitivity and resolution are improved by 2 orders of magnitude, allowing nonperturbing measurements to be made at densities below 10 7 cm -3. In addition to a description of the technique, sample measurements of time-resolved wave induced modifications of ion velocity distributions are shown. P ACS numbers: 52.25.Fi, 52.70.Kz
A tapered-wiggler free-electron-laser oscillator has been operated above threshold at the wavelength of 1.57 jum. The laser was operated with 0%, 1% , and 2% tapers in energy, achieving laser efficiency of 0.4%, 1.1%, and 1.2%, respectively. The efficiency of the 2% taper was three times the untapered case.
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